1. Field of the Invention
The present invention relates to an apparatus and method for enhancing the quality of reproduced images, and more particularly, to an apparatus and method for enhancing the quality of reproduced, progressive images, which are capable of obtaining more natural and smoother progressive images and preventing such problems as blurry colors and aliased images that could be brought about in the process of converting interlaced images into progressive images.
2. Description of the Related Art
A variety of methods of converting an interlaced image into a progressive image (e.g., Korean Patent Application No. 10-1999-7012311 (PCT/US 98/12816)) have already been suggested. Among those methods, a blending method and an edge dependent interpolation method, in particular, will be briefly described in the following paragraphs.
In a blending method, the value of a predetermined pixel is obtained through interpolation by using an interlaced-scanned value of a predetermined input pixel and values of pixels vertically adjacent to the predetermined input pixel. This technique can guarantee smoother and more natural representation of an image, especially, edges of subjects on the image. However, when applied to the case of converting an interlaced image, containing subject's swift motions, into a progressive image, the blending method may undesirably provide a blurry or aliased image or an afterimage.
In an edge dependent interpolation method, an interpolated pixel value is obtained using the values of pixels vertically and horizontally adjacent to a predetermined pixel to be interpolated, a process which is apparent in FIG. 1. As shown in FIG. 1, a progressive-scanned value X′ of a predetermined pixel X is obtained using values Dlu, Dld, Dru, Drd, Vu, and Vd of upper left, lower left, upper right, lower right, upper, and lower pixels, respectively, with respect to the predetermined pixel X.
More specifically, the progressive-scanned pixel value X′ is obtained through interpolation using a smaller value among Vu−Vd, Dlu−Drd, and Dld−Dru. Since this technique takes the values of the pixels, diagonally adjacent to the predetermined pixel X, into account, it can successfully provide more natural and smoother representation of images, especially, slant lines and subject edges on those images, while preventing the images from being aliased.
However, in the case of the conventional edge-dependent interpolation method, there is a great possibility of errors occurring in the process of determining a direction, toward which a slant line representing an edge included in a predetermined input pixel is tilted. In addition, since either odd or even fields of an interlaced image are practically abandoned, it is more likely to see a huge saturation difference between the interlaced image and a corresponding progressive image. Moreover, in the case of converting an interlaced image, containing subjects' swift motions, into a progressive image, colors of an output image may spread undesirably. The conventional edge-dependent interpolation method is taught by Gerald De Haan in Deinterlacing: An Overview, Proceeding of the IEEE, Vol. 86, No. 9, September, 1998.